Adsorption method for separating metal cations



J. X. KHYM March 10, 1959 ABSORPTION METHOD FOR SEPARATING METAL CATIONSFiled May 9, 1948 INVENTOR. aa'epfl 2: x& ym

United States Patent ABSORPTION METHOD FOR SEPARATING METAL CATIONSJoseph X. Khym, Santa Fe, N. Mex., asslgnor to the United States ofAmerica as represented by the United States Atomic Energy CommissionApplication May 9, 1946, Serial No. 668,636

23 Claims. (Cl. 23-23) This invention relates to the separation ofsubstances by means of chromatographic adsorption, and in particular toa method of separating cations contained in a solution which involvesadsorbing the cations upon an adsorbent and selectively eluting thedesired cations from the adsorbent.

As described herein, the isotope of element 94, having a mass of 239, isreferred to as 94 and is also called plutonium, symbol Pu. In addition,the isotope of element 93 having a mass of 239 is referred to as 93" andis called neptunium, symbol Np. Furthermore, the term values or itsequivalent when employed herein with reference to an element is intendedto embrace the element and compounds thereof. For example, the termcolumbium values is intended to include columbium as well as compoundsthereof. The term activity or its equivalent when employed herein withreference to a radioactive element is intended to include theradioactive element and compounds thereof. For example, the termcolumbium activity as employed herein is intended to include radioactivecolumbium as well as compounds thereof.

Naturally occurring uranium contains a major portion of U a minorportion of U and small amounts of other substances such as UX, and UXWhen a mass of such uranium is subjected to neutron irradiation,particularly with neutrons of resonance or thermal energies, U bycapture of a neutron becomes U which has a half life of abouttwenty-three minutes and by beta decay becomes 93 The 931 has a halflife of about 2.3 days and by beta decay becomes 94 Thus, neutronirradiated uranium contains both 93 and 94 but by storing irradiateduranium for a suitable period of time, the 93 is converted almostentirely to 94 In addition to the above mentioned reaction, the reactionof neutrons with fissionable nuclei such as the nucleus of U results inthe production of a large number of radioactive fission products. Forexample, when an atom of U undergoes fission, two fragments are formed.These fragments vary sufliciently in their masses and hence their atomicnumbers to give some 34 elements, all of which initiate further reactionchains with the emission of radiations. These chains are the source ofall of the radioactivity that renders isolation of any one of theproducts of irradiation of uranium so dilficult. The radiations include:(1) beta or high speed negative electrons with variable energy contents,and therefore, different velocities, (2) soft gamma, or electro-magneticradiation similar to X-rays but with a shorter wave length andmoderately higher energy content, (3) hard gamma similar to the softtype except that it has a shorter wave length and higher energy content,and (4) neutrons.

In general, the stability of an atom depends on the ratio of protons toneutrons in the nucleus and certain ratios, therefore, result in anexcess energy content 2,877,094 Patented Mar. 10, 1959 ice that must beemitted as radiation before a stable end product is formed. While mostnaturally occurring isotopes are stable and therefore not radioactive,those resulting from fission have proton-neutron ratios such as to causeinternal instability. As a result, they tend to stabilize and in theprocess emit their excess energies in one of five general ways.

In the first place, an atom may emit a beta particle from the nucleuswhere the only possible source of a negative electron is from a neutronwhich gives both a positive and negative charge. The loss of thenegative charge converts the neutron to a proton and there is a gain ofone in atomic number and hence a transmutation to the next higherelement. Such a change, of course, alters the proton to neutron ratioand may result in a stable atom, although this is not necessarily true.

In the second place, a beta particle of lower energy content may beemitted, thus forming the next higher element while still leaving thenucleus with too great an energy content to be stable. The first betaparticle may then be followed by another one to form the second higherelement in the atomic series which again may or may not be stable.

Thirdly, a beta particle of intermediate energy may be emitted to forman unstable isotope of the next higher element which, due to its excessenergy, may give off a gamma ray rather than a beta particle. Thisprocess also may result in either a stable or an unstable atom.

Fourthly, the beta-decay of a fission product may leave the nucleus in astate of excitation higher than the binding energy of a neutron in thatnucleus. The neutron is then immediately emitted, and the rate of decayof the neutron-emitting activity observed is just that of the precedingbeta activity.

Finally, an unstable atom may emit a gamma ray which strikes an electronin one of the inner shells of electrons and ejects it in such acondition that it has some of the properties of the nuclear betaparticle. Since the electron, which in this case is known as photoelectron, does not originate in the nucleus, there is no change in theatomic number and the process, like that involved in the emission of agamma ray, is known as internal conversion.

With the exception of elements 43 and 61, the fission products formed bythe above discussed reaction are all well known elements with normalchemical properties, the only point of difference between them and thenatural element being that they are composed of unstable isotopes. Asbrought out above, due to their internal instability they either undergotransmutation to other elements or stabilize themselves internally bythe emission of one or more of the previously-mentioned radiations.Consequently, stabilization may involve no change in atomic number or achange of several units. The average length of the fission chains, thatis the number of transmutations, is about 3.2 but some may be as long as6. In general, a chain reaction has emitted a total of 25 to 30 m. e. v.as radiation by the time it is complete.

The fission of U yields two general types of elements, namely heavy andlight. The light fission products possess atomic numbers between 30 and46 and include radioactive zinc, gallium, germanium, arsenic, selenium,bromine, krypton, rubidium, strontium, yttrium, zirconium, columbium,molydenum, 43, ruthenium, rhodium, and palladium.

The heavy fission products resulting from neutron irradiation of Upossess atomic numbers ranging from 47 to 63 and include radioactivesilver, cadmium, indium, tin, antimony, tellurium, iodine, xenon,cesium, barium,

lanthanum, cerium, praseodymium, samarium and europium.

Generally speaking, the irradiation of uranium is conducted under suchconditions as result in the combined amount of neptunium and plutoniumbeing equal to approximately 0.02% by weight of the uranium mass. Theconcentration of the fission products in neutron irradiated uranium isapproximately the same as that of the total of the plutonium andneptuuium. However, since many of the fission products are radioactive,they change to other elements at certain fixed rates which arecharacteristic of each fission product. In other words, they have fixeddecay rates. Plutonium, on the other hand, is relatively stable, andsince the fission products have varying decay rates, the concentrationof the initially formed radioactive fission products with respect toplutonium changes substantially during the course of the reaction andparticularly during the storage period which is generally employed afterthe neutron irradiated uranium has been removed from the reaction zone.

The quantities of the various individual radioactive fission productspresent in neutron irradiated uranium are extremely small and aregenerally referred to in the art as "tracer quantities.

As used herein, the terms tracer" and tracer quantity" or theirequivalents are employed as definitive of extremely small amounts ofradioactive materials. For example, radioactive materials inconcentrations of to 10- molar are considered to be tracer quantities.Such extremely small amounts are incapable of identification by ordinarymicro analytical methods, and are, therefore, generally identified bythe radiations emitted therefrom by means of any of the usual countingmechanisms known to the art.

As illustrative of a typical neutron irradiated mass containing fissionproducts the following tables are given:

TABLE A Distribution of beta activity in neutron irradiateduraneodymium, 61,

TABLE B Distribution of effective gamma activity in neutron irradiateduranium for each fission element as percentage of total Cooling TimeElement 30 Days 60 Days 100 Days As illustrative of the method ofobtaining the data for the above tables, the following is given.

sion product solution is subjected to counting and is found to have atotal beta activity of 453,000 counts/ minute/milliliter. To a 1.00 ml.sample is added 20.0 mg. of Ru and by appropriate chemical manipulationthe Ru is isolated and purified. The final precipitate of metallic Ruweighs 18.0 mg. and gives 4950 counts/ minute. The chemical yield istherefore and the count, corrected for chemical yield, is 5500counts/minute or 1.21% of the total activity.

From the above tables it can be seen that certain fission products arelisted as both beta emitters and gamma emitters. This situation resultsfrom the presence in neutron irradiated uranium of various isotopes ofthe elements which comprise the fission products. Thus, one isotope ofan element may be a beta emitter while another isotope may be a gammaeitter. Furthermore, and as is more generally the case, certain of theisotopes may emit both types of radiation.

Some members of both the light and heavy groups of fission products maybe readily separated from the neutron irradiated uranium mass in thatthey have been found to have chemical properties similar to the rareearths and can, therefore, be isolated by precipitation under carefullycontrolled conditions with about one hundred times their weight ofcarriers such as lanthanum fluoride, bismuth phosphate, and the like.However, many of the fission products in both groups do not re spond tosuch treatment and considerable difiiculty has been experienced not onlyin attempting to separate plutonium values from these fission products,but also in attempting to isolate certain of the fission product valuesin carrier-free radioactive form.

It can be seen from the above discussion that the separation andisolation of the various products formed as a result of the neutronirradiation of uranium is an extremely difficult task, particularly inview of the fact that extremely small quantities of the individualfission products are present in the materials under treatment. Theproblem is further complicated by the presence of the various isotopesand the fact that the elements, considered to be formed at the time offission, may actually represent conversion products from certain of thefission product which have undergone extremely rapid change; that is,those fission products having extremely short half lives. In thisconnection, approximately isotopes of the fission products involved havebeen identified and about 30% of these have half lives of over eighthours. Fission products have been identified that have half livesranging from about 3 seconds to 10 years.

Since, as pointed out above, the fission product values contained in asolution of neutron irradiated uranium even after a considerable periodof storage exhibit radioactive properties, it is particularlyadvantageous not only to separate these fission product values fromplutonium values, but it is also advantageous in certain instances toisolate certain of the fission product values in carrierfree radioactiveform in that they serve as an excellent source of radioactivity whichmay be utilized in various fields such as medicine and metallurgy.

I have found that selected components of a solution may be separated andrecovered by a process which involves passing the solution through anadsorbent under conditions favoring the adsorption of the selectedcomponents and selectively eluting said components from the adsorbent.

It is accordingly an object of my invention to provide a process ofseparating selected components of a solution by adsorption and selectiveelution.

It is a further object of my invention to provide a simple process ofseparating radioactive components of a solution which process is capableof remote control.

It is still another object of my invention to provide a simple remotelycontrollable process of separating radio- A mixed fis- 75 activecomponents of a solution which process may be utilized in conjunctionwith other methods of separating the components of radioactivesolutions.

These and other objects of my invention will become apparent to thoseskilled in the art upon becoming familiar with the following descriptionwhen taken in conjunction with the accompanying drawing which dia'grammatically illustrates a system which may be utilized in the practiceof my invention.

Referring to the drawing, 1 designates a column containing a suitableadsorbent 2. Above column 1 is located tank 3 which is connected tocolumn 1 by line 4 controlled by valve 6. To the upper portion of tank 3are connected line 5 controlled by valve 6', line 7 controlled by valve8 line 9 controlled by valve 10 and line 1]. controlled by valve 12.

Passage from the bottom of column 1 is provided by line 13 whichconnects to line 14 controlled by valve 15 and line 16 controlled byvalve 17.

In operation of the system described above, a solu tion containing thecomponents to be separated is passed through line 5 into tank 3 whereinthe condition of the solution is adjusted to favor adsorption of theselected components by adsorbent 2 in column 1. This condi tion isattained by the admission of suitable reagents through any one of lines7, 9 or 11. When the desired condition has been reached, valve 6 in line4 is opened and the solution is allowed to flow through column 1 and thedesired components are removed by adsorbent 2, the remaining solutionpassing through lines 13 and 14 to disposal, valve 17 in line 16 beingclosed.

Following the adsorption of the selected components in the mannerdescribed above, these components are selectively eluted by means of theadmission of various reagents into tank 3 through any one of lines 7, 9and 11 and passage of the conditioned reagents through line 4 into andthrough column 1 containing adsorbed material on adsorbent 2. With valve15 in line 14 closed, the eluate is passed through line 16, valve 17being open, to storage or to any desired destination.

The solutions which may be processed in accordance with my invention aresubject to wide variation. However, the invention is particularlyadaptable to the separation of fission products contained in a solutionof neutron irradiated uranium. The solution under process may containuranyl nitrate hexahydrate together with fission products. When such asolution is treated, it is generally the practice to remove UO by meansof dilute sulfuric acid or other sources of 80,. In such a process, theUO is eluted before passage of any eluting agent selective for anyfission products through the column.

Another solution which may be treated in accordance with my invention isthat resulting from the ether extraction of uranyl nitrate hexahydratesolution. In the ether extraction process, UO is extracted from thesolution containing the uranyl nitrate hexahydrate by means of ether andthe residue is then contacted with water to obtain a water solution offission products; such a water solution may also be processed for therecovery of individual fission products or of groups of fission productsin accordance with my invention.

Generally speaking, a wide variety of adsorbents may be utilized incolumn 1 for the selective adsorption of components of the solutionunder treatment. When dealing with the separation of fission productsfrom a solution of neutron irradiated uranium. particularly advantageousresults have been obtained by the use of ion exchange adsorbents, inwhich the cation of the adsorbent is exchanged for a similarly chargedion of the substance to be adsorbed. It has been found that the processis particularly effective where the adsorbent used is a relatively inertorganic material containing free sulphonic acid groups. Thus, theadsorbent may comprise phenol-formaldehyde resins, iignite,phenol-tannic acid resins, or the like, which contain numerous RSO,-R'groups in which R is an organic group such as a methylene group and inwhich R is hydrogen or a metal ion, although R is preferably H+ or Na' Aparticularly satisfactory adsorbent which may be employed is aphenol-formaldehyde condensation product containing methylene sulphonicacid groups (--CH SO H). In the adsorption process, the hydrogen of thesulphonic acid group is replaced by a cation of the substance to beadsorbed which thereupon forms a more of less loosely associatedmolecule with the residue.

As an example of a method by which a sulphonated resin may be prepared,175 parts of l-hydroxy-benzene- 4-sulphonic acid are heated togetherwith 40 parts of a formaldehyde solution of 30% strength for one-halfhour to about 105 C. Then, further, 60 parts of formaldehyde are addedand the temperature is kept for about 10 hours at C. A hard black resinis formed which is stable to water and of conchoidal fracture. Thisresin is washed with water and ground to a powder. By regeneration withan acid or a solution of common salt, this base-exchanging body regainsits original adsorption capacity.

Generally speaking, the eluting agents utilized in the practice of myinvention may be varied, depending, among other things, upon theparticular component to be eluted, and the conditions of elution.However, generally speaking, particularly advantageous results may beobtained by employing polycarboxylic acids and salts thereof as elutingagents. Examples of such eluting agents are oxalic acid, citric acid,tartaric acid, sodium citrate, sodium tartrate, potassium citrate,potassium tartrate, ammonium citrate, and ammonium tartrate.Particularly advantageous results are obtained by employing ammoniumsalts of polycarboxylic acids such as ammonium citrate and ammoniumtartrate in that the positive ion NHp can be conveniently destroyed suchas by aqua rcgia.

In one embodiment of my invention, a solution con taining the componentsto be separated and recovered, such as a solution containing fissionproducts resulting from neutron irradiated uranium is passed throughcolumn 1 containing an adsorbent such as an ion exchange resin having aplurality of -CH SO H groups and the fission products adsorbed areselectively eluted by successive washes of the resin bed with differenteluting agents. Certain groups of fission products or certain individualfission products are eluted by certain of the eluting agents and therebyrecovered and the remaining groups of fission products or individualfission products are eluted by other eluting agents.

This embodiment of my invention is illustrated by the following specificexamples.

EXAMPLE I 200 cc. of a mixture of fission products was prepared byadmixing solutions of tracer in accordance with the following table:

TABLE C Total Tracer No. no counts per second Zr and Ch 4o 41, 500 Cs 4044,300 40 sasoo 40 19.600 40 45,600

This synthetic mixture of fission products was then passed through a cc.adsorption column containing an ion exchange resin characterized byhaving a plurality of --CH SO H groups. Following adsorption of thefission product activities, the column was then washed with 100 cc. ofwater. Thereafter the adsorbent bed was washed with 150 cc. of 1% oxalicacid. The eluate was collected and analyzed and found to contain 94% ofthe Cb and Zr activity originally present. The adsorbent bed was thenwashed with 100 cc. of water and thereafter 825 cc. of 5% tartaric acidcontaining ,4: equivalent of NH OH was passed through the columns. Theeluate was collected and analyzed and found to contain 96% of the Ce andY activity originally present. 100 cc. of water was then passed throughthe adsorbent bed and thereafter the adsorbent was washed with 235 cc.of 3 N HCl. The eluate was collected and analyzed and found to contain96% of the Ba and Sr activity originally present.

In accordance with another embodiment of my invention a solutioncontaining the components to be separated and recovered, such as asolution containing fission products resulting from the neutronirradiation of uranium, is passed through a column containing a suitableadsorbent such as an ion exchange resin having a plurality of -CH S Hgroups, and the adsorbed fission products are selectively eluted bywashing the adsorbent bed with the same eluting agent employed atvarying pHs. Certain of the fission products are eluted at a particularpH whereas the other fission products are eluted by the same elutingagent at a different pH.

This embodiment of my invention is illustrated by the following specificexample:

EXAMPLE II A solution containing Y and Ce activity was passed through acolumn containing a 0.65 cm. x 60 cm. bed of a 40 to 60 mesh ionexchange resin characterized by having a plurality of -CH3SO3H groupsresulting in the adsorption of the activities by the resin. 8 columnvolumes of a 4.75% solution of ammonium tartrate at a pH of 2.9 werepassed through the column. The eluate was collected and identified ascontaining Y as 94% of the activity present. About 15 column volumes ofammonium tartrate solution at a pH of 2.8 was passed through the column.The eluate was collected and identified as containing Ce as 95% of theactivity present.

The embodiments of my invention outlined above may be combined to obtaina more efiicient separation of the components of a solution, if such aseparation is desired. For example, certain of the components of asolution may be separated by utilizing a different eluting agent and theremaining components may be separated by uti lizing the same elutingagent at different pHs.

This modification of my invention is illustrated by the followingspecific examples:

EXAMPLE III 200 ml. of a fission product mixture obtained by the etherand water extraction of a nitric acid solution of an 80 day old 1 kg.neutron irradiated uranium slug was passed through a 100 ml. columncontaining a 100 cm. x 1 cm. bed of a 40-60 mesh ion exchange resincontaining a plurality of -CH SO H groups at a rate of about 1 to 5 ml.per minute. The ion exchange resin containing adsorbed activity was thenwashed with about 300 ml. of water and thereafter washed with about 200ml. of 0.25 N H 80 to insure removal of any uranium values present. Theadsorbent bed was then washed with about 700 ml. of water and thereafterwith 200 ml. of /2% oxalic acid. The eluate was collected and analyzedand found to comprise approximately'99.4% Zr and Cb activity, the ratioof Zr to Cb being approximately 3 to 1. Following the removal of theabovcmentioned activities. 800 ml. of 4.75% ammonium citrate at a pH of2.9 was passed through the column over a period of approximately 8hours. A cut was taken between the sixth and seventh hour of elution andanalyzed and the Y activity was found to be 98.9% of the total activitypresent. A second cut was taken between approximately the seventh andeighth hour of elution and analyzed and found to contain Y as 71.8% ofthe total activity present.

Following elution of the activities as indicated above, approximately600 ml. of a 4.75% ammonium citrate solution at a pH of 3.3 was passedthrough the column over a period of about 5 hours. A cut was takenbetween the second and third hour of elution and analyzed and found tocontain more than of the activity present in the form of Ce activity.

EXAMPLE IV A 200 ml. solution of fission products obtained by the etherand water extraction of a nitric acid solution of a 40 day old 1 kg.neutron irradiated uranium slug was passed through a ml. resin columncontaining a 100 cm. x 1 cm. bed of a 40-60 mesh ion exchange resincharacterized by having a plurality of CH SO H groups at a rate ofapproximately 1-2 ml. per minute. The adsorbed material was then washedwith about 300 ml. of 0.5 N H 80 to remove any uranium values which mayhave been present. About 250 ml. of 0.5% oxalic acid were passed throughthe column and the eluate was collected. Analysis of this eluateindicated that all of the activity present therein was attributable toZr and Ch. The adsorbent bed was then washed with 535 ml. of a 5%ammonium tartrate solution at a pH of 2.7. The last 100 ml. of eluate toflow from the column was collected and analyzed. This cut was found tocontain Y in the amount of 95% of the activity present. The column wasthen washed with about 500 ml. of 5% ammonium tar trate solution at a pHof 2.9. Approximately the second 200 ml. of eluate from the column wascollected and divided into a ml. out which was analyzed and found tocontain Ce as approximately 75% of the total activity present and a 60ml. cut which was analyzed and found to contain Ce as approximately 94%of the total activity present. The final 63 ml. of eluate from thecolumn was analyzed and found to contain Ce as 99% of the activitypresent. The column was then washed with a 5% ammonium tartrate solutionat a pH of 3.1, the eluate was analyzed and the first 260 ml. thereofwas found to contain Ce as 99% of the total activity present. Thereaftera 5% solution of ammonium citrate at a pH of 5.0 was passed through thecolumn and after a 185 ml. of efiiuent had come off the column the next45 ml. upon analysis showed Sr as 99% of the activity present. The nextfollowing 108 ml. of eluate upon analysis showed Sr at 94% of theactivity present. After the passage of about 350 ml. of eluting agentthrough the column, the eluate upon analysis showed Ba as 99% ofactivity present.

EXAMPLE v A 520 ml. solution of mixed fission products obtained by theether and water extraction of a nitric acid solution of a 30 day old 1kg. neutron irradiated uranium slug was passed through a 100 ml. resincolumn containing 100 cm. x l cm. bed of 40-60 mesh ion exchange resincharacterized by having a plurality of -CH SO H groups. The adsorbedmaterial was washed with 410 ml. of 0.5 N H 80 to remove any uraniumvalues which may have been present. The adsorbed material was thenwashed with about ml. of /2% oxalic acid, the next 60 ml. of eluate wasanalyzed and found to contain Zr and Cb as 99.9% of the activitypresent, the bulk of which was in the form of Zr. Thereafter theadsorbed material was washed with about 300 cc. of 7% oxalic acidsolution and the eluate analyzed and found to contain approximately 85%of the activity in the form of Cb with the preponderant portion of theremaining activity being in the form of Zr.

The resin bed was then washed with about 1600 ml. of a 5% ammoniumcitrate solution at a pH of 2.75. The first 800 ml. of effiuent showedlittle activity but the next 400 ml. of effluent upon analysis indicatedthat Y constituted approximately 98.3% of the activity. The next 265 ml.of efiluent upon analysis indicated Y as approximately 97.8% of theactivity. Following the pass sage of the above-mentioned 1600 ml. ofeluting agent approximately 950 ml. of ammonium citrate at a pH of 3.35was passed through the column. After approximately the first 200 ml. ofeifluent had passed from the column, the next 350 ml. of effiuent uponanalysis indicated that Ce constituted approximately 97.7% of the totalactivity present. The next 250 ml. of effluent upon analysis indicatedthe activity present to be comprised of approximately 86% Ce.

The resin bed was then washed with approximately 600 ml. of 5% ammoniumcitrate at a pH of 4.76. The first 380 ml. of effluent from the columnupon analysis indicated that Sr constituted approximately 90% of thetotal activity present. The last 220 ml. of effluent upon analysisindicated that Ba constituted approximately 90% of the total activitypresent.

In still another embodiment of my invention separation of components ofa solution may be made by differential rates of elution from anadsorbent bed. For instance, in case of barium and strontium it has beenfound that barium may be eluted more rapidly than strontium at the samepH. This pH is one of which barium is eluted in higher percentage thanstrontium. The two can be separated completely therefore if a longcolumn and a large volume of eluting agent are employed. It is alsopossible to utilize a short column and a small volume of eluting agentto give a degree of separation which would be practically complete ifrepeated frequently enough. The separation of components by differentialrate of elution is illustrated in the specific example V in the laststep where barium and strontium are separated by differential rate ofelution. The following example is also illustrative of this embodimentof my invention.

EXAMPLE VI 125 cubic cm. of an ion exchange resin containing a pluralityof -CH SO H groups was suspended in distilled water and transferred toan upright glass tube 1 cm. in diameter and allowed to settle. Astopcock was inserted in the bottom of the glass tube by means of arubber stopper covered with stainless steel gauze to allow liquid topass through the column at the desired rate and to keep the resin frompassing out. About 500 ml. of 6 N HCl was then passed through the columnto convert the resin to its acid form. The column was washed withdistilled water until liquid leaving the column had the same pH as thewater entering the column. A solution of a mixture containing Pr, Nd,I1, and a trace of Y activity was passed through the column at a rate of1 to 2 ml. per minute. The column was then Washed with about 100 to 200ml. of distiled water. The column was then washed with a 5% ammoniumcitrate solution at a pH of 2.75 which was prepared by dissolving 50 g.of citric acid in 100 ml. of distilled water and adding enoughconcentrated NH OH to efiect the desired pH. The eluting agent waspassed through the column at the rate of about 1 ml. per minute. Thefirst portion of the efiiuent from the column was analyzed and found tocontain approximately 90% of the original 11 present. The second portionof the elfiuent was analyzed and found to contain approximately 90% ofthe Nd present. The third portion of the eifiuent was analyzed and foundto contain approximately 90% of the Pr activity originally present.

It is also possible within the scope of my invention, as illustrated byExample V, to utilize all of the abovemention methods of selectiveelution in the separation of the components of a solution.

Another method of selective elution which may be employed in thepractice of my invention is that involving varying the concentration ofeluting agent while maintaining a uniform pH.

Generally speaking, the invention is particularly adapt able to theseparation of metal cations especially those cations which occur asfission products in the preparation of radioactivities either with orwithout added inactive carriers. The process of the invention is equallyeffective for the separation of mixtures of, or individual fissionproducts. Generally speaking, the preferred pH for the initial andeluting solution will depend on the acid used, on the adsorbent used andon the cations to be adsorbed; ordinarily the adsorption solution willhave a lower pH than the eluting solution, for instance l-3 foradsorption as compared to 3 to 6 for elution.

In the practice of my invention, it is particularly advan tageous toremove any excess acid such as tartaric or citric acid which may beadsorbed, particularly where tracer quantities are involved. Such aremoval may be accomplished by washing the adsorbent with distilledWater which procedure removes the excess acid without removing thedesired cations.

When ammonium ion is present in the eluting agent or complcxing agent,the adsorbate in the column is generally contaminated therewith. Shouldremoval of NHJ' be desired, it may be accomplished by washing theadsorbate with 3-6 N HCl. Such a procedure also removes other inactivecations such as iron, aluminum and the like which may be present in thefinal adsorbate.

An alternate procedure for removal of NH;+ is to remove the cations fromthe body of adsorbent with 3-6 N HCl and thereafter destroy the NH bythe addition of aqua regia to the eluate.

The desired activity may be separated from the eluting agent byevaporating the eluate liquid to dryness thus isolating the activity asthe salt of the acid employed in the eluting agent.

While the invention has been particularly described with reference tothe separation of the components of a solution of neutron irradiateduranium, it is to be understood that other types of solutions may beseparated by means of the process of the invention. For example, theinvention may be applied to the separation of rare earths as well as tothe separation of N from neutron -irradiated thorium. The invention mayalso be applied to the separation of cyclotron bombarded materials.

While the above description makes particular mention of the separationof cations, the process of the invention may also be utilized in theseparation of anions. One method of separating anions is that involvingthe utilization of an adsorbent selective for anions such as an anionexchange resin. In some instances, the anions of the desired componentsmay be converted to cations and processed in a manner similar to thatabove described.

In the specification and claims the following terms have the followingmeanings.

The term efiluenf or its equivalent is intended to include any materialcoming off of the columns.

The term eluate" or its equivalent is intended to include any effiuentbearing a desired product from a column.

The term eluting agent" or its equivalent is intended to include amaterial which removes activity from a column.

The term adsorption is utilized in referring to removal of componentsfrom the solution. It is to be understood, however, that the inventionis not to be limited in any sense by the theory upon which the processis based and that this term is used as it is generally employed in theart of chromatographic separation.

While the invention has been described with reference to certainparticular embodiments and with reference to certain specific examples,it is to be understood that the invention is not to be limited thereby.Therefore, changes, omissions, and/or additions may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims which are intended to be limited only as required by the priorart.

I claim:

1. A process of separating the components of a mixture of fissionproduct metal cations containing zirconium, columbium, cerium, yttrium,barium, and strontium cations, which comprises passing a solution ofsaid cations through a granulated mass of an ion exchange resincharacterized by having a plurality of -CH SO H groups, eluting saidzirconium and columbium by means of oxalic acid, eluting said cerium andyttrium by means of tartaric acid, and eluting said barium and strontiumby means of hydrochloric acid.

2. A process of separating yttrium and cerium cations from a solutioncontaining the same which comprises passing said solution through agranulated mass of ion exchange resin characterized by having aplurality of CH=SO H groups, passing a solution of ammonium tartrate ata pH of approximately 2.9 through said resin, thereby eluting saidyttrium, and thereafter passing a solution of ammonium tartrate at a pHof approximately 2.8 through said resin, thereby eluting said cerium.

3. A process of separating the components of a mixture of fissionproduct metal cations containing zirconium, columbium, cerium andyttrium cations which comprises passing a solution of said mixturethrough a granulated mass of an ion exchange resin characterized byhaving a plurality of CH SO H groups, passing a dilute solution ofoxalic acid through said resin thereby eluting said zirconium andcolumbium, passing a dilute solution of ammonium tartrate at a pH ofapproximately 2.9 through said resin thereby eluting a preponderantportion of said yttrium, and passing said dilute solution of ammoniumcitrate at a pH of approximately 3.3 through said resin thereby elutingthe preponderant portion of said cerium.

4. A process of separating the components of a mixture of fissionproduct metal cations containing zirconium, columbium, yttrium, cerium,barium and strontium cations which comprises passing a solution of saidmixture at a pH less than 3 through a body of granulated ion exchangeresin characterized by having a plurality of --CH-,-SO H groups, washingsaid resin containing adsorbed fission products with a dilute oxalicacid solution thereby eluting the preponderant portion of said zirconiumand columbium, thereafter washing said resin containing adsorbedmaterial with a dilute ammonium tartrate solution at a pH ofapproximately 2.7 thereby eluting the preponderant portion of saidyttrium, washing said resin containing adsorbed material with a furtherquantity of said ammonium tartrate solution at a pH of approximately2.9, thereby eluting the preponderant portion of said cerium, andthereafter washing said resin containing adsorbed material with afurther quantity of said ammonium tartrate solution at a pH ofapproximately 5.0, thereby initially eluting from said resin saidstrontium and finally eluting from said resin said barium.

5. In a process of separating radioactive fission product metal cationsincluding yttrium cations from a solution containing the same whichcomprises adsorbing said fission product cations upon an ion exchangeresin characterized by having a plurality of CH SO H groups andselectively eluting said fission products from said resin; the stepcomprising passing through said resin containing adsorbed fissionproducts an aqueous solution containing up to 5% by weight of a compoundselected from the group consisting of ammonium tartrate and ammoniumcitrate adjusted to a pH between about 2.7 and 2.9 thereby selectivelyeluting said yttrium.

6. In a process of separating radioactive fission product metal cationsincluding cerium cations from a solution containing the same whichcomprises adsorbing said fission product cations upon an ion exchangeresin characterized by having a plurality of CH SO H groups andselectively eluting said fission products from said resin; the stepcomprising passing through said resin containing adsorbed fissionproducts a dilute aqueous solution of a compound selected from the groupconsisting of ammonium tartrate and ammonium citrate adjusted to a pH ofapproximately 2.9 to 3.3 thereby selectively eluting said cerium.

7. In a process of separating radioactive fission product metal cationsincluding barium cations from a solution containing the same whichcomprises adsorbing said fission product cations upon an ion exchangeresin characterized by having a plurality of -CH SO H groups andselectively eluting said fission products from said resin; the stepcomprising passing through said resin containing adsorbed fissionproducts a dilute aqueous solution of a compound selected from the groupconsisting of ammonium citrate and ammonium tartrate adjusted to a pH ofabout 5 thereby selectively eluting said barium.

8. A process for the separation of fission-product metal cations from anaqueous solution containing the same, which comprises contacting saidsolution with a comminuted mass of ion-exchange adsorbent to therebyeffect adsorption of said fission-product cations thereupon, andthereupon contacting the resulting fission-product-bearing adsorbentwith a dilute aqueous solution of a salt of a polycarboxylic acid, tothereby elute said fission products from the adsorbent therewith.

9. The process of claim 8 wherein said salt of a polycarboxylic acid ischosen from the group consisting of ammonium, sodium, and potassiumsalts thereof.

10. The process of claim 8 wherein said salt of a polycarboxylic acid isan ammonium polycarboxylate.

11. The process of claim 8 wherein said salt of a polycarboxylic acid isammonium tartrate.

12. The process of claim 8 wherein said salt of a polycarboxylic acid isammonium citrate.

13. The process of claim 8 wherein said ion-exchange adsorbent is anion-exchange adsorbent resin having a plurality of -CH=SO H groups.

14. The process of claim 8 wherein said aqueous solution of a salt of apolycarboxylic acid is an approximately 5% by Weight solution of anammonium polycarboxylate.

15. The process of claim 8 wherein said aqueous solution of a salt of apolycarboxylic acid is a solution, having a pH within the approximaterange of pH 2.7 to 6, of an ammonium polycarboxylate.

16. A process for the separation of rare earth metal cations from anaqueous solution containing the same, which comprises contacting saidsolution with a comminuted mass of an ion-exchange adsorbent, to therebyeffect adsorption of said rare earth cations thereupon, and thereafterpassing through the resulting rare-earth hearing mass of adsorbent anaqueous solution of a salt of a polycarboxylic acid chosen from thegroup consisting of ammonium, sodium, and potassium salts thereof, tothereby elute said rare earth from the adsorbent mass therewith.

17. A process for selectively separating constituent species offission-product metal cations from an aqueous solution containing thesame, which comprises passing said solution through a body of comminutedion-exchange adsorbent resin to thereby efiect adsorption of saidfissionproduct cations thereupon, and thereafter passing through theresulting fission-product-bearing adsorbent body a succession ofdifferent eluants, at least one of which comprises an aqueous solutionof a salt of a polycarboxylic acid chosen from the group consisting ofammonium, sodium, and potassium salts thereof, to thereby effectselective elution from the adsorbent of fission-product speciestherewith.

18. A process for selectively separating constituent species offission-product metal cations from an aqueous solution contacting thesame, which comprises passing said solution in a substantiallyunidirectional flow through a bed of comminuted ion-exchange adsorbentresin to thereby effect adsorption of fission-product cations thereupon,thereafter passing through the resulting fissionproduct-bearingadsorbent bed, in substantially the same direction as the flow ofsolution during adsorption, an aqueous solution of a salt of apolycarboxylic acid chosen from the group consisting of ammonium,sodium, and potassium salts thereof, to thereby elute difierentfissionproduct species at difierential rates through said bed,

13 and collecting successive fractions of the resulting eluate, eachrich in a respective fission-product species.

19. A process for selectively separating constituent species offission-product metal cations from an aqueous solution containing thesame, which comprises passing said solution through a body of comminutedion-exchange adsorbent resin, to thereby etfect adsorption offissionproduct cations thereupon, and thereafter passing through theresulting fission-product-bearing body of adsorbent an aqueous solutionof a salt of a polycarboxylic acid chosen from the group consisting ofammonium, sodium, and potassium salts thereof, while progressivelyincreasing the pH thereof, to thereby selectively elute particularfission-product species with different pH's of said salt solution.

20. A process for selectively separating constituent species offission-product metal cations from an aqueous solution containing thesame, which comprises passing said solution through a body of comminutedion-exchange adsorbent resin, to thereby effect adsorption offissionproduct cations thereupon, and thereafter passing through theresulting fission-product-bearing body of adsorbent an aqueous solutionof a salt of a polycarboxylic acid chosen from the group consisting ofammonium, sodium, and potassium salts thereof, while progressivelyincreasing the polycarboxylate concentration thereof, to thereby selectively elute particular fission-product species with dif ferentpolycarboxylate concentrations of said salt solution.

21. A process for selectively separating different rare earth metalcations from an aqueous solution containing a plurality of the same,which comprises passing said solution, in a substantially unidirectionalflow, through a bed of comminuted ion-exchange adsorbent resin, tothereby effect adsorption of said rare earth cations thereupon,thereafter passing through the resulting rare-earthbearing adsorbentbed, in substantially the same direction as the flow of solution duringadsorption, an aqueous solution having a pH within the approximate rangeof pH 2.7 to 6, of a salt of a polycarboxylic acid chosen from the groupconsisting of the ammonium, sodium, and potassium salts thereof, tothereby elute the ditferent adsorbed rare earth species at differentialrates through said adsorbent bed, and thereafter collecting successivefraction of the resulting eluate each rich in respective rare earthspecies.

22. The process of claim 21 wherein said aqueous solution of a salt of apolycarboxylic acid is a solution having a pH of approximately 3, of anapproximately 5 percent by weight concentration of ammonium citrate.

23. The process of claim 21 wherein said aqueous solution of a salt of apolycarboxylic acid is a solution. having a pH of approximately 3, of anapproximately 5 percent by weight concentration of ammonium tartrate.

References Cited in the file of this patent Thompkins et al.: Journal ofthe American Chemical Society," vol. 69, pp. 2769-2777, 1947.

Spedding et al.: Journal of the American Chemical Society," vol. 69, pp.2777-2781, 1947.

Smyth: A General Account of the Development of Methods of Using AtomicEnergy for Military Purposes Under the Auspices of the U. S. Government,1940-4945, p. 19, publ. 1945 by U. S. Govt. Printing Oflice.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2,877,094 March 10, 1959 Joseph X. Khym It is hereby certified thaterror appears in the-printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 4, line 2, for the numeral "453,000" read 453,600 line 16, after"gamma" for "eitter" read emitter column 8, line 46, after "Sr" for "at"read as column 9,, line 51, for "distiled" read distilled column 10,line 37, for "N read U column 1;

line 65, for "contacting" read containing Signed and sealed this 25thday Of August 1959.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. A PROCESS OF SEPARATING THE COMPONENTS OF A MIXTURE OF FISSIONPRODUCT METAL CATIONS CONTAINING ZIRCONIUM, COLUMBIUM, CERIUM, YTTRIUM,BARIUM, AND STRONTIUM CATIONS, WHICH COMPRISES PASSING A SOLUTION OFSAID CATIONS THROUGH A GRANULATED MASS OF AN ION EXCHANGE RESINCHARACTERIZED BY HAVING A PLURALITY OF -CH2SO3H GROUPS, ELUTING SAIDZIRCONIUM AND COLUMBIUM BY MEANS OF OXALIC ACID, ELUTING SAID CERIUM ANDYTTRIUM BY MEANS OF TARTARIC ACID, AND ELUTING SAID BARIUM AND STRONTIUMBY MEANS OF HYDROCHLORIC ACID.